Two-speed resin systems are well-known for anchoring mine bolts and tendons to provide roof and side wall support in mines. In particular, the resin systems are provided in capsules which are inserted into boreholes and subsequently punctured in a manner such that the contents are mixed and then allowed to solidify. The capsules may include two compartments. A first compartment may include both fast and slow speeds of a reinforced, thixotropic, polyester resin mastic (a fluid), while a second compartment may include an organic peroxide catalyst (also a fluid). The resin and catalyst are segregated from one another in the capsule so that reaction is prevented prior to puncturing of the compartments. Capsules housing a variety of ratios of fast to slow speed resins are commercially available, for example in ratios of 50% fast to 50% slow or 40% fast to 60% slow speeds. The use of two-speed resins permits bolt pre-tensioning. The “faster” speed mastic is disposed toward one end of the capsule while the “slower” speed resin is disposed toward the other end. As used herein, the term “mastic” means liquid component with filler. For example, there can be resin mastic (liquid component plus filler) as well as catalyst mastic (liquid component plus filler).
In order to puncture the capsule so that the contents of the compartments may be released and mixed, a bolt (or other reinforcing member) abutting a capsule for example may be rotated in place to shred the capsule, mix the components, and permit solidification of the mastic. The capsule is inserted into the borehole so that the “faster” end abuts the top of the hole thereby permitting a bolt inserted into the borehole to be anchored by the solidified mastic at the top of the hole first. The orientation of the capsule in the borehole (“faster” end inserted first) is important to the success of the anchoring medium to provide support. In particular, once the bolt has been anchored at the top of the borehole, a nut may be tightened at the opposite end of the bolt to apply a compressive force to an associated support plate abutting the mine roof surface to in turn compress the sagging mine roof. In order to successfully compress the region of the mine roof adjacent the bolt, the mastic should not anchor the bolt except at the top end of the borehole, until after the nut has been sufficiently applied. Only then should the “slower” speed resin disposed toward the other end of the bolt fully solidify to anchor the remaining portion of the bolt. In order to distinguish which end of a capsule contains the “higher” speed resin, a colorant may be added to one or more of the resins as an identifying feature. Such pigmenting or coloration thus can serve as indicia of gel time.
The resin capsules are available in a variety of lengths ranging from 2 feet to 6 feet and in diameter from ¾ inch to 1¼ inch.
Typically, in the United States, resins for mine roof supports are purchased in a pre-inhibited or pre-promoted condition. For example, the base resin typically may have a 20 minutes gel time, which may be adjusted through the addition of inhibitors and promoters. In other words, the polyester resins are purchased with a desired gel time which optionally may be adjusted using inhibiters and promoters to slow down or speed up, respectively, the gel time. The gel time of the resin is known as the time for the resin to set up, e.g., typically from 10 seconds to 2 minutes and in the United States, typically either 10 seconds, 30 seconds, 60 seconds, or 120 seconds. More particularly, as explained in U.S. Pat. No. 4,280,943 to Bivens et at entitled “Organic Grouting Composition for Anchoring a Bolt in a Hole,” the entire content of which is incorporated herein by reference thereto, the gel time of a resin formulation as used herein is defined as the time that elapses between the mixing of the reactive components and the hardening or stiffening of the resin in the mixture (e.g., the mixture of resin and initiator/catalyst). The gel time is shorter at higher temperatures and/or with higher promoter content, and vice versa. Gel time testing will be discussed separately herein.
As used herein, the cure time of a resin formulation, as explained in U.S. Pat. No. 4,280,943, is the time required for the composition to achieve full strength, or a high percentage of its final strength, with a desirable goal being that the composition attain about 80% of its final strength in an hour or less. It is known that it is especially important that as strong as possible an interfacial bond be achieved between the resin and the wall of the hole, and the resin and the reinforcing member, during the curing period. In particular, the advantageous keying effect achieved by shifting of rock strata relative to one another usually is not available during this period because the roof has only recently been exposed.
ASTM Designation F 432-94 entitled “Standard Specification for Roof and Rock Bolts and Accessories” provides a Speed Index for chemical grouting materials which “indicates the time in seconds from completion of mixing until an anchorage level of 4000 lb is achieved when tested” in accordance with the laboratory test specified in the Standard. According to the Standard, grout formulations are identified in accordance with the speed index classification system in Table I below, where the Maximum Cure Time is to achieve a 4000-lb test load:
TABLE ISpeed IndexMaximum Cure Time (s)1515303060602402406006001000>600
Despite the availability of a standard and its associated testing regime for determining Maximum Cure Time, however, the testing regime is fairly rigorous and thus time consuming and not easy to precisely follow, and concomitantly can be costly. Moreover, while the ASTM standard for example might indicate that a particular grout formulation meets a Speed Index of 15 which correlates to a Maximum Cure Time of 15 seconds, this information does not reveal the progress of a grout formulation toward solidification over a shorter period of time. In other words, while a particular formulation may be determined to meet a Speed Index of 15, the formulation may reach a gel state substantially faster than 15 seconds and this may be undesirable in a given application. As an example, it may be desired for a bolt to “set up” within 15 seconds, but not much faster than 15 seconds. Once the bolt grouting “gels,” the bolt can't readily be maneuvered in the borehole because of the substantial viscosity of the grouting.
As used herein, the terms “grouting,” “grouting system,” “grout,” and “grout system” mean a substance that hardens to anchor a reinforcing member in a space. For example, grouting can be provided in the form of a cartridge with a compartment housing a polyester resin and a compartment housing an initiator/catalyst, such that when the cartridge is shredded and the resin is mixed with the initiator/catalyst, a reinforcing member can be anchored in a space.
Both the Speed Index under the ASTM standard and gel time remain important, however. This is because even though a grout may have gelled, the grout may not have cured to the point that it can support a 4000-lb test load as required under the ASTM standard for purposes of safety.
In the United States, for example, the current practice is to purchase polyester resin from a manufacturer in a pre-promoted state. The acquired resin has a specific gel time, which subsequent to purchase may be adjusted by the purchaser using promoters or inhibitors to speed up or slow down the gel time to meet desired needs. For example, a formulation designated Speed Index 240 would have a Maximum Cure Time of 240 seconds, but the purchaser can add a promoter to the formulation to change the Speed Index to 180 which corresponds to a Maximum Cure Time of 180 seconds. Such Speed Index adjustment (which generally correlates with gel time adjustment) using a promoter thus is done in a batch-wise fashion, requiring an entire batch of resin to be consumed before making an additional gel time change (this is because a formulation can't be repeatedly promoted, then inhibited, then again promoted, etc., with the expectation that the addition of substantial additions of inhibitor won't effect the formulation's ability to cure or that the gel time can be increased at any point as desired). Additionally, gel time is dependent on the resin to catalyst ratio. According to this approach, if there is more catalyst the gel time is faster, and conversely if there is less catalyst the gel time is slower.
In a manufacturing operation, for example, resin initially may be supplied by a resin supplier with a gel time of 10 seconds. However, the manufacturer may desire to have 500 gallon capacity tanks of resin at gel times of 10 seconds, 30 seconds, and 60 seconds. Thus, 500 gallons of the 10 second resin may be pumped into a tank and mixed with inhibitor or promoter to make a batch of 30 second resin. Typically, once the 500 gallons of 30 second resin has been made, however, cartridges are formed until that batch has completely been consumed.
Nonetheless, it would be unusual for a purchaser to acquire resin associated with a gel time of 10 seconds, for example, and then batch-wise add inhibitor to modify the gel time associated with that resin to 60 seconds. This is because resin already is available in the United States as a standard product offering for a gel time of 60 seconds. Also, it is unusual to use inhibitor to adjust gel time, in general, because polyester resin for example is typically manufactured with a standard gel time on the order of 20 minutes; subsequently, promoter, which is costly, is added to the resin to make it faster. It then doesn't make sense to spend even more money to subsequently make the resin slower by adding inhibitor. By analogy, like use of an automobile's accelerator and brakes, it doesn't make any sense to “floor it” with the accelerator (make the resin much faster by adding promoter) and then adjusting the speed only using the brakes (make the resin slower by adding inhibitor). This compares with a “normal” method of driving an automobile in which speed increases are made by incremental increases in use of the accelerator pedal; normally, with resins, the speed is incrementally adjusted by adding promoter.
It is common to start with resin that has a 20 minute gel time, and then promote the resin to have a gel time of 60 seconds.
It also is common to have resin with a gel time of 10 seconds and inhibit the resin to a gel time of 20 seconds, or to have resin with a gel time of 30 seconds and inhibit the resin to a gel time of 45 seconds. But with respect to the former, for example, even with a gel time of 20 seconds, the resin would have a Speed Index of 30 seconds, meaning that a mine operator could not put load on a bolt potted with the resin for a full 30 seconds rather than 20 seconds.
To adjust gel time for mine roof support grouting systems, therefore, it is known to inject promoter into the resin. It also is known to separately manufacture two different batches of resins with each batch having a different gel time and separately pumping each of the two resins into a film cartridge so as to obtain a two-speed grouting system cartridge. In order to differentiate which end represents a particular resin speed, a dye is often included with at least one of the resins, but unfortunately the resin is somewhat dark in color and thus the addition of the dye can be difficult to discern. Using colorant in the resin requires significantly more colorant than using it in the inhibitor. This is because the resin is darker and more colorant therefore is needed to make a significant difference visually because the contrast change is small. Also, in a two resin cartridge, for example, seventy percent of the volume of the cartridge can be associated with the resin while 30% can be associated with the catalyst. Thus, in comparison, over twice the amount of colorant can be required because when coloring resin because there is over twice the amount of resin as compared to catalyst.
The primary roof support systems used in coal mines include headed rebar bolts typically 4 feet to 6 feet in length, ¾ inch and ⅝ inch in diameter, and used in conjunction with resin grouting in 1 inch diameter holes.
Typically, grouting is accomplished using multi-compartment resin cartridges. A variety of such cartridges are known disclosed in U.S. Pat. No. 3,861,522 to Llewellyn, U.S. Pat. No. 4,239,105 to Gilbert, and U.S. Patent Application Publication No. US 2007/0017832 A1 to Simmons et al. As discussed above, the multi-compartment cartridges are designed to keep the polymerizable resin and catalyst separate from each other until the cartridge, when inserted in a borehole, is intentionally ruptured by a mine roof bolt that also is inserted in the borehole. When the resin and catalyst are mixed (by virtue of rupture as well as spinning of the bolt in the borehole) and subsequently harden, the bolt is held in place.
In some prior art devices and methods for forming partitioned film packages such as multi-component resin cartridges, a series of cartridges are formed and then cut at a clipping head associated with the package-forming apparatus or in a separate operation from the cartridge forming operation, i.e., off-line using a cutter separate from the clipping head. In particular, the cartridges are separated from one another proximate their clipped ends, i.e., proximate the regions of the opposite ends of the cartridges which are each clipped so as to retain the resin and catalyst in the package. Thus, before being separated, adjacent cartridges have two clips adjacent each other with some cartridge packaging disposed therebetween. A cut is made between the adjacent clips to separate the cartridges.